GLOSSARY


Pressure Gauge Terminology

Absolute Pressure

The pressure of a system is defined as the force exerted by the system on a unit area of its boundaries, typically pounds per square inch. Absolute pressure is referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure (14.7 psi).

Accuracy

The conformity of an indication to its true value. Accuracy is a percentage of the full scale value. So, a 0/160 psi gauge with ±1% full scale accuracy means that the gauge will be accurate to within plus or minus 1.6 psi.

Ambient Conditions

The environmental conditions (pressure, temperature, etc.) of the medium surrounding the instrument.

Bourdon Tube

Pressure gauge operating principal

The majority of pressure gauges in use today have a bourdon tube as a measuring element. The bourdon tube itself is thinly waved into a semicircle (C-shaped) or spiral.

The bourdon tube works by sensing pressure and converting that pressure into displacement, so as pressure is applied through the socket, the bourdon tube straightens itself causing the precision movement to shift upward, or downward for vacuum measurements. The movement then transforms the motion of the bourdon tube pointer which indicates the inputted pressure.The bourdon system is analog based and does not require any additional power sources.

Winters’ pressure gauges measure full vacuum (Hg), compound and pressure ranges up to 20,000psi. They are suitable for all clean and non-clogging liquids and gaseous media.

C-tubes

The C-shaped bourdon tube has a hollow, elliptical cross section. It is closed at one end and connected to the fluid pressure at the other. When pressure is applied, its cross section becomes more circular, causing the tube to straighten out, until the force of the pressure is balanced by the elastic resistance of the tube material. A pointer is attached to the closed end of the tube through a linkage arm and a gear and pinion assembly, which rotates the pointer around a graduated scale.

Helical Bourdon Tube

Helical bourdon tubes are used for measuring pressure above 1000psi.

Capsule Type

When in operation, the capsule will move in proportion to the difference in pressure applied across the capsule unit assembly. The linear motion of the capsule is picked up by a drive arm and transmitted as a rotary motion through a torque tube assembly. The indicating mechanism multiplies the rotation of the torque tube through a gear and pinion to the indicating pointer. Because of the elasticity in both the capsule and spring in a spring-loaded capsule element, the relationship between the applied pressure and capsule movement is linear.

Burst Pressure

The maximum pressure that can be applied to the bourdon tube without rupturing it or causing leakage in a transmitter.

Can

The housing which covers the electronic components of a transmitter. The majority of our products will have 316 stainless steel can/housing, although, other materials such as brass and carbon steel are available.

Differential Pressure

The measured difference between two separate but related pressures.

Drift

The change in accuracy of a pressure reading over time. A transmitter can gradually go out of calibration after continued use which is called “drift”. The amount of drift experienced by a transmitter may or may not have an effect on the customers’ application. If little or no drift is a major requirement, be sure to note this so that the correct unit can be supplied.

Excitation

The external electrical voltage and/or current applied to a transducer for its proper operation.

Electrical Connection

The connection on the transducer/transmitter used to attach the wires.

Gauge Pressure

Pressure measured relative to ambient atmospheric pressure. This is normally what is measured by Winters pressure gauges.

Hysteresis

The maximum difference in output, at any measured value within a specified range, when the value is approached first when increasing and then decreasing pressure.

Linearity

The maximum deviation of any calibration point, on a specified straight line, during any one calibration cycle.

Life Cycle

The number of times an instrument can provide a pressure measurement within its specified accuracy tolerance through the full range.

Proof Pressure

The maximum pressure that can be applied to the transmitter without a permanent change in the performance of the unit.

Process Connection

The connection that is used to connect the instrument to the process it is measuring. The standard type of connection that Winters uses is NPT (National Pipe Thread).

Range and Reference Point

When a transducer or transmitter is ordered, the pressure range required must be specified as well as the electrical signal (output). In a transmitter, where a range is given as 0–100psi with a 4–20mA output, the pressure reading of 0psi equals 4mA and the pressure of 100psi equals 20mA (the maximum electrical signal).

Repeatability

The ability to reproduce output readings when the same pressure value is applied consecutively, under the same conditions and in the same direction.

Response time

The length of time required for the output to rise to a specified percentage of its final value, as a result of a steep change in pressure.

Thermal Error

The maximum change in output, at any pressure value within the specified range when the temperature is changed from room temperature to specified temperature extremes.

Thermal Sensitivity Shift

The sensitivity shift due to changes of the ambient temperature from room temperature to the specified limits of the operating temperature range.

Thermal Zero Shift

The zero shift due to changes of the ambient temperature from room temperature to the specified limits of the operating temperature range.

Transducer

A device that takes mechanical force (pressure) and converts it to an electrical energy. In the case of our product offering, a transducer will be a unit with a voltage output (i.e. 1-5 Vdc, 0-5 Vdc, etc.).

Transmitter

A device that takes mechanical force (pressure) and converts it to an electrical energy. The output signal will be milliamp output (4-20mA) rather than voltage output. Note: A transmitter may also be considered a transducer, but a transducer with strictly a voltage output should never be considered a transmitter.

Vacuum

Vacuum measured relative to ambient atmospheric pressure, which is 14.7 psi. So, any pressure that is under 14.7 psi is considered vacuum, and is usually measured as inches of mercury (inHg).

Zero/Span Adjustment

This allows the operator to adjust the unit to read a known pressure (i.e. 0 or 100 psi) so that the unit can be adjusted/calibrated in the field.

Pressure Transmitter Terminology

Accuracy

Accuracy can be expressed along several different parameters, but the most common is as a percentage of full-scale output (FSO). Accuracy can range from 1% FSO down to 0.01% depending on your requirements. When needed, external zero and span adjustment controls can be added to the transmitter, allowing for fine tuning of the unit.

Can

The housing which covers the electronic components of a transmitter. The majority of our products will have 316 stainless steel can/housing, although, other materials such as brass and carbon steel are available.

Pressure Connection Port

Some common types of connections are: 1/4” or 1/2” NPT thread, 1/4” SAE, sanitary, flush, submersible, BSPT autoclave, and VCR, among many others. The size of the connection should also be considered.

Electrical Connector

There are various electrical connectors. Some common connector types and brands you will encounter including: DIN 43650, Mini-DIN, Turck, Packard, Lumberg, Submersible, Bendix PTIH-8-4P, 1/2” conduit and terminal block.Environment It may be important to consider whether or not a corrosive agent will come into contact with the transmitter. If this is the case, it will be necessary to ensure that the can (housing) of the transmitter is made with a suitable material such as stainless steel.

Output

There are various electrical connections involving transmitters. The most common output signals are: milliamp (4-20mA), volts (0-5VDC, 1-5VDC, 0.5-4.5VDC, 0-10VDC), and millivolts per volt (100, 200, 300mV/V).

Sensor

There is a wide variety of sensor technologies to choose from: sputtered, thin flim, CVD, bonded strain gauge, ceramic capacitance, piezo-resistive and piezo-electric. Each has its own performance advantages.

Signal Conditioner

The signal conditioner converts the sensor’s natural signal to a desired output. Also special circuitry can be added to protect the signal from interference.

Temperature

Temperature is a variable that affects the overall performance of a transmitter, particularly its accuracy. Temperature compensation circuitry is added to correct for the inherent temperature induced error. If needed, the unit can be compensated to allow it to operate at elevated temperatures.

Pressure Switch Terminology

Actuation Point (commonly referred to as a setpoint)

The actuation point is expressed in terms of exact pressure at which the snap-action switch is actuated to either open or close the electrical circuit (depending on how the switch is wired).

Adjustable Range

Actuation range within which the actuation point of a pressure actuated switch may be adjusted.

Deadband

The deadband is the difference between the actuation point and the reactuation point in a pressure switch. For example: if a pressure switch is set to operate at 200 psi on increasing pressure, the switch will actuate when pressure rises to that point. As the pressure drops to 190, the switch actuates again (this is the reactivation point). The deadband of this switch is 10 psi (the difference between the setpoint of 200 and the reactivation point of 190 psi).

Electrical Switching Element

The electrical switching element in a pressure switch opens or closes an electrical circuit in response to the actuating force it receives from the pressure sensing element.

Pressure Sensing Element

A pressure sensing element is the portion of the pressure switch that moves due to a change in pressure.

Pressure Switch

A pressure switch is an instrument that automatically senses a change in pressure and opens or closes an electrical switching element when a predetermined pressure point is reached.

Repeatability (Accuracy)

The ability of a pressure switch to repetitively operate at its setpoints. For example: if a pressure switch that is set to actuate at 200 psi repeatedly actuates from 199 to 201 psi, it is considered to be repeatable within plus or minus 1%.

System Pressure

The rated pressure of a hydraulic or pneumatic system which does not include the maximum surges that the system may encounter.

Tolerance

Tolerance is the normal variation in production pressure switches of the same specifications. It affects the actuation value and the reactuation point and not the accuracy of the setpoint.

Working Pressure

The pressure range a switch may see under normal working conditions. This is commonly referred to as the adjustable range.

Variable Pressure

A fluctuating pressure having characteristics of sufficient magnitude to operate a pressure actuated switch. This pressure is usually the one that is sensed by a pressure switch.

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